A turbojet generally includes a fan, one or more compressor stages, for example a low pressure compressor and a high pressure compressor, a combustion chamber, one or more turbine stages, for example a high pressure turbine and a low pressure turbine, and an ejection nozzle. In the combustion chamber, compressed fuel is injected and burned with the compressed air originating from the compressors. Each compressor is integral in rotation with a turbine, to which it is connected by a shaft, thus forming a high pressure body and a low pressure body.
The combustion chamber is supplied with fuel by a fuel injection circuit including a fuel pump including a low pressure stage and a high pressure stage.
The concepts of low and high pressure of the fuel pumps are totally non-correlated with the concepts of low and high pressure of the bodies of the turbojet, concerning the pressure of different fluids; by convention, and to simplify the description, the acronym “HP” will be used for “high pressure” in the following description, and the acronym “LP” for “low pressure”, both for the bodies of the turbojet or their elements and for the fuel pumps.
The HP stage of the fuel pump receives, in normal operation, a sufficient pressure at its inlet in order to function. The pressure at the inlet of the HP stage is guaranteed by the LP stage of the pump. The role of the HP stage is to deliver a flow of fuel which is sufficient to supply the combustion chamber and the variable geometries of the complete fuel system. The fuel pump also includes a pressure relief valve allowing the flow leaving the HP stage to be recirculated towards the inlet of the HP stage when the difference in pressure between the inlet and the outlet of the HP stage is too great. This pressure relief valve is generally an internal component of the fuel pump which connects the inlet to the outlet of the HP stage. This pressure relief valve is generally in closed position, but if the difference in pressure between the inlet and the outlet of the HP stage is too great, it opens so as to prevent damaging the HP stage. The pressure relief valve therefore opens more or less as a function of the difference in pressure between the inlet and the outlet of the HP stage. This pressure relief valve is therefore essential.
However, in the case of pollution, of cold, or in the case of rapid opening of the pressure relief valve, the latter can remain locked in the open position, which results in a total or partial recirculation of fuel and prevents the injection of fuel in the combustion chamber and the supplying of the variable geometries of the system. The normal functioning of the system is therefore no longer assured. However, currently, no detection device of a breakdown of the relief valve is provided in turbomachines. Also, in the case of a breakdown of the motor, due to a failure of the pressure relief valve, the maintenance teams have to dismantle all the equipment and test it so as to be able to identify the origin of the breakdown. The maintenance teams have to, in particular, dismantle the fuel pump and inspect it. This operation is long and complicated, and it can prove to be useless in the case where the breakdown of the motor is not due to a breakdown of the pressure relief valve.